550 5.4.1 Recipient address rejected: Access denied
Microsoft 365 rejected an unknown recipient at the edge
Seen in Microsoft 365, Exchange Online Protection
Directory Based Edge Blocking in Exchange Online rejected the message because the recipient address does not exist in the receiving tenant.
Common causes
- The recipient address is mistyped or no longer exists.
- A new user or alias has not synced to Exchange Online yet.
- The domain is set as Authoritative in Microsoft 365 while some mailboxes still live on another mail system.
How to fix it
- Confirm the exact address with the recipient.
- If it is your tenant, check the user or alias exists in Exchange Online and that directory sync has completed.
- If some mailboxes are hosted elsewhere, set the accepted domain to Internal Relay and add an outbound connector for them.
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Related errors
- 550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP · Microsoft 365 blocked the tenant's outbound mail
- 530 5.7.57 Client not authenticated to send anonymous mail during MAIL FROM · The app sent to smtp.office365.com without logging in
- 535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant · Microsoft 365 refused the SMTP AUTH login
- 550 5.7.520 Access denied, Your organization does not allow external forwarding · Automatic forwarding to an outside address is blocked
- 550 5.1.8 Access denied, bad outbound sender · The sending account was blocked for spam
- 451 4.7.500 Access denied, please try again later · Microsoft 365 is temporarily throttling the sending IP
- 552 5.2.2 The recipient's inbox is out of storage space · The recipient's mailbox is full
- 552 5.3.4 Your message exceeded Google's message size limits · The message is larger than the server accepts
- 535 5.7.8 Username and Password not accepted · The SMTP login was rejected
- 450 4.2.0 <user@example.com>: Recipient address rejected: Greylisted · The message was greylisted; it will be accepted on retry
- 553 5.7.1 <user@example.com>: Sender address rejected: not owned by user · You logged in as one user but sent as another address
- 530 5.7.0 Must issue a STARTTLS command first · The server requires TLS before it accepts mail